Fitness trackers didn't always monitor sleep, but the feature is now a sought-after staple in most devices, as sleep is just as important as exercise to a healthy lifestyle. Most wristbands monitor sleep now, and there are even specialized devices that go on your head or bedside table that can also keep track of how long and how well you sleep each night.

But sleep tracking isn't as simple as step tracking, and you need more than a simple accelerometer to measure it accurately. While motion is an indicator, it's not the only metric you should track to get a full picture of how well you slept.

What makes a good night’s sleep?

Understanding how well you slept on any given night depends on your time in light, deep, and REM sleep. Light sleep occurs soon after you fall asleep and your heart rate and body temperature go down. Your body falls into deep sleep typically after 10 to 15 minutes of light sleep, and this is when the body repairs itself from the day before. You'll spend most of your night in light and deep sleep, as REM sleep periods tend to be shorter.

REM sleep is the stage we hear about most often because it's known as the stage in which we dream. Since the brain is more active during REM sleep than the other two stages, your body changes during REM, increasing your heart rate and brain activity while your eyes move rapidly as you dream. The longest REM sleep phase can last an hour, but the body builds up to that amount of time. The first time you enter REM sleep after going to bed could last just ten minutes, but as the night goes on, your body enters longer periods of REM sleep.

It's important to experience all three sleep stages, which is why getting enough time to sleep is crucial. Typically, we experience light, deep, and REM sleep as a cycle, and we go through multiple sleep cycles each night. If you only have three or four hours of rest, you may not fit in enough sleep cycles for your body to fully repair itself from the day before. While the recommended number of hours of sleep per night varies by age, the National Sleep Foundation recommends seven to nine hours of sleep per night for regular adults ages 26 to 64.

Just as important as sleep stages is the number of times you wake up during the night. While some of us are dead to the world when we sleep, only to be awakened by the blaring sounds of an alarm, others wake up frequently. In fact, even the heaviest of sleepers can be technically awake at points during the night and not even know it. However, waking up for long periods of time, or waking up multiple times each night, can be disruptive to the entire sleep process and your productivity the next day. Aside from diagnosable sleep disorders, a number of things can wake you in the middle of the night, including too many alcoholic drinks before bed, not enough exercise throughout the day, and spending too much time on your phone or tablet before turning off the lights.

How can you track your sleep at night?

Considering the nuanced differences between sleep stages, it's tricky for modern wearables to accurately track sleep. Let's first talk about devices like Fitbit's Alta HR wristband. Most such devices use accelerometers to track movement both when you're awake and when you're asleep. However, if you're a naturally restless sleeper or someone who moves around a lot during the night, nighttime movement data can be deceiving. Wearables assume that if you're moving around at night, you're probably not sleeping as soundly as you could. For some people, that might be true, as many sleep disorders are characterized by excessive movement during sleep. However, not all movement during sleep is bad, and a certain level of it is natural.

Further Reading

Medical professionals and users have been vocal about movement being only one factor that determines a good night's sleep, so companies have recently incorporated information from other sensors to inform sleep data. For example, the Alta HR is the first device Fitbit released that uses nighttime heart rate data to estimate light, deep, and REM sleep time. A lot of devices that track sleep have optical heart rate monitors, but it's often unclear if that data is used to bolster sleep-tracking data. The Alta HR released with improved sleep tracking as a highlighted feature (and that feature came to other Fitbit devices with heart rate monitors in an OTA update soon after), and it uses heart rate and heart rate variability, or the variations between individual heart beats, to estimate changing sleep stages.

Then there are other types of smart health devices that claim to capture data similar, and in addition to, wearables like the Alta HR. Beddit, which was recently acquired by Apple, makes a strip-like mattress cover that captures movement, heart rate, humidity, and temperature information while you sleep. While it might seem like a more comfortable option than a wristband, that could be a disadvantage: for those who move while asleep, it won't have as much close and consistent contact with your body the entire night like a wristband would. That could also be a problem for bedside devices like the ResMed S+, a box-like device that uses non-contact, respiratory, and bio-motion sensors to track your sleep habits as well as the light, temperature, and noise levels in your bedroom.

While some of these devices use medical research and science to inform their sleep tracking methods and algorithms, it's important to note that none of them are certified medical devices. As a 2015 study published in the Dove Press Nature and Science of Sleep journal states, "The claims are not intended to be 'medical' in nature, such that the validation standards normally applied to medically used devices are not required." Since a Fitbit isn't a medical device, users shouldn't expect to be able to diagnose a sleep disorder from its data, much less use it as a replacement for seeing a medical professional. However, some sleep trackers may be better than others at obtaining accurate information about how we sleep.

Not using a tracker myself, but my parents both use one (without heart rate function) for about half a year now. They're around 65 of age.

The funny thing about having a good night sleep is that believing you had a good night of sleep holds placebo properties. My parents often complained about the many hours they were awake at night, never sleeping more than a couple of hours. Sure, I threw some youtube videos that explained that the hourse/interval of sleep change during one's lifetime, but that didn't really help to ease them. But these trackers did, in a sort of roundabout way.

They see the graphs and notice the discrepancy with what they believe was a bad night of sleep, and this seems to have helped them become more accepting of what a good night of sleep entails. As we all know, thinking about how tired we're going to be next morning during the night is a sureway to keep yourself awake. LIke, what they believed was an hour being awake shows up as just a quarter of an hour. If the graph in total shows them having had 5+ hours of actual sleep they're satisfied with their night! And that's what it shows them most of the time during the morning synchronisation.

Sure, they understand that these nightly recordings need to be taken with a grain of salt (as they know it is based on movement alone), and I'm not going to inform them on the new details I've learned from this article.

As a gadget curious person, I've tried a few different sleep tracking devices, and I've even used more than one at once. Guess what? They can come to wildly different conclusions, and after some research, I learned that sleep tracking devices are basically stopwatches with delusions of grandeur.

Here is what matters:

First, focus on sleep quality that doesn't cost you time:1a) Stop eating/drinking hours before bed. Alcohol makes for especially low quality sleep.1b) Have peaceful sleep. No noise, no light, and no distractions (phones/books/TV/etc).1c) Get regular sleep. It helps you fall asleep faster and make the best of what time you have.

Next, accept that sleep is win-win, not zero sum:2a) Get enough sleep. It helps you be more productive/happy in the remaining hours.2b) Exercise. Really. People that exercise regularly need less sleep than those that don't.2c) Get your weight under control. Being overweight is hard on the body and bad for sleep.

Ironically, I quit wearing my watch to bed because my wrist swells up and the band becomes tight enough to become uncomfortable enough to wake me up. But when I did wear it at night I used a sleep tracker app. It didn't work all that well and the activity app would often register several hours of standing. I'm almost certain I don't sleepwalk (and an OS upgrade seems to have stopped that anyway), but for a few nights I was a little concerned.

Let's also not forget that the current trend of "8 hours uninterrupted sleep" might not be what some of our bodies like to do.

There was an interesting article in the BBC back in 2012 that looked at sleep patterns over history, and found that "humans used to sleep in two distinct chunks" and that "During this waking period people were quite active. They often got up, went to the toilet or smoked tobacco and some even visited neighbours. Most people stayed in bed, read, wrote and often prayed. Countless prayer manuals from the late 15th Century offered special prayers for the hours in between sleeps"

Some historic quotes:

"He knew this, even in the horror with which he started from his first sleep, and threw up the window to dispel it by the presence of some object, beyond the room, which had not been, as it were, the witness of his dream."Charles Dickens, Barnaby Rudge (1840)

"Don Quixote followed nature, and being satisfied with his first sleep, did not solicit more. As for Sancho, he never wanted a second, for the first lasted him from night to morning." Miguel Cervantes, Don Quixote (1615)

"And at the wakening of your first sleepe You shall have a hott drinke made, And at the wakening of your next sleepe Your sorrowes will have a slake." Early English ballad, Old Robin of Portingale

"Few headband sleep monitors exist for consumers—there's the Zero personal sleep coach and Sleep Shepard, and a few like the iBand+, which are trying to crowdsource their funding."

That Zeo Personal Sleep Coach and they went out of business years ago. I got one of the early models, and I thought it was wrong in measuring my sleep... Turns out 10 year later that I have minor sleep apnea.

I was given a fitness tracker thingy for free, so I started wearing it. It will track my sleeping (as well as it does) but, other than glancing at it every couple days, I don't really pay attention to it. I don't actively try to sleep more or less than normal, it's just a kind of interesting game that my wife and I compare to see who woke whom up in the middle of the night.

I have to wonder how many times it's caught on a pillow or sheet and made me turn/shift where it I didn't have anything I might not have....

There's an interesting iOS app, called autosleep, that takes your motion & HR data from your Apple Watch from over night and does it's sleep calculations. You don't even have to use an app on your watch, so it's pretty convenient. I suppose it might also be able to do something with the data collected just by your phone if you don't have a watch, but I'm not sure.

But they're still not advanced enough to track everything you'd need to track in order to assess how well you slept.

Not to dismiss a well sourced and well-written article, but almost every consumer device on the market is imperfect and involves tradeoffs of one kind or another.

My watch tells the time well enough, these sleep trackers apparently don't track sleep all that well.

It's not about trade-offs, they don't accurately do what they tell you they can do.

No, that's not true.

They do provide some information about your sleep, and that information has been valuable to some. We had this same article/discussion about step counters.

It works for some. It doesn't work for others.

And that's ok.

Well many, like my Garmin don't track sleep, but motion. My Garmin reported 7 hours of "sleep" after a night of full insomnia. The following night I slept like a log and awoke refreshed, and it reported 6 hours of "sleep".

IMO, mine is utterly useless.

It's a real sleep tracker when it can read brain waves to detect REM and other stages of sleep.

I am kind of curious how bad the device's sensors are versus the software. I wear a Garmin Fenix all the time and I was trying to get a resting heart rate (taken right after I wake up) but found the number the built-in HR sensor gave was vastly different from wearing a strap. So, I pulled a data-dump and looked at the raw numbers. I found that the data was not that different, between the strap and wrist sensor, but the software had some kind of logic that if the heart rate, read from the wrist, dropped below 59bps it would not use that to update low or average data fields. So, I would get a resting heart rate of 42 wearing the strap and recording to another Garmin, 59 with the wrist strap and built-in software or 45 with some HR software I tossed together using the wrist sensor.

I work as an ent specialist in a university Sleep lab. We see patients for full polysomnography with tons of electrodes etc. and even then I occasionally have to turn on the video stream to correlate sleep states to the telemetry. Our patients are often sent by private practices that use screening devices significantly more elaborate than the fitness and sleep trackers and the results are still often full of artifacts.

The likelihood of artifacts and false data is very high in these devices as a pure consequence of the lack of input. I'm not sure it's sensible to imply that the data output is reliable or should be used to judge sleep quality.

Edit: to make my point more clear: I think the article conclusion is to optimistic.

However, these devices can act as more affordable alternatives for those curious about how well they sleep night in and night out. You can learn basic information about your sleep habits from some wearables, the best of which are those with onboard heart rate monitors that track pulse at night.- It's not easy for consumer devices to track sleep well, but there are some available that monitor heart rate and motion well enough to provide informative data about your sleeping style.

I'm sorry, but sleep trackers (and to an extent, fitness trackers) fall into the "solution looking for a problem" category. They inundate consumers with a ton of pseudo-data with no clear way of utilizing or interpreting it. No one realized that sleep data was missing from their life until a company came along and told them, and not they've been convinced that it's integral to their wellbeing.

I'm sorry, but sleep trackers (and to an extent, fitness trackers) fall into the "solution looking for a problem" category. They inundate consumers with a ton of pseudo-data with no clear way of utilizing or interpreting it. No one realized that sleep data was missing from their life until a company came along and told them, and not they've been convinced that it's integral to their wellbeing.

This.

How do you know you have a sleep problem? 'cause you're constantly tired despite spending 9+ hours in bed per night. There's no need for a sleep tracker for the general public.

While the same stands true for stuff like, GPS watches for runners, etc, at least there it holds a purpose to guide our intentional training. Tracking one's sleep... just seems futile unless there's something seriously out of step. ...and if there's a need to collect specific, individual data, there should likely be a medical professional involved.

The only real use I see for something like this is in sleep studies themselves. On the individual level, this just seems a futile thing beyond sating one's curiosity.

I've tried sleep tracking with a number of devices. I have a ton of sleep issues I wont bore anyone with but needless to say, none of the trackers I used worked consistently. I also found myself leaning towards the tracker that confirmed my bias as to how I slept, either well or badly.

Additionally, wearing something while sleeping is irritating. My wife has an advantage in that she just clips her old fitbit to her bra but for me it's basically on my wrist or nothing, which is uncomfortable when I sleep with my hand under the pillow or near my face.

The advantage to sleep data for me would simply be to know what I did that was most effective to actually fall asleep, and then stay that way for a prolonged time.

I work as an ent specialist in a university Sleep lab. We see patients for full polysomnography with tons of electrodes etc. and even then I occasionally have to turn on the video stream to correlate sleep states to the telemetry. Our patients are often sent by private practices that use screening devices significantly more elaborate than the fitness and sleep trackers and the results are still often full of artifacts.

The likelihood of artifacts and false data is very high in these devices as a pure consequence of the lack of input. I'm not sure it's sensible to imply that the data output is reliable or should be used to judge sleep quality.

Edit: to make my point more clear: I think the article conclusion is to optimistic.

Too optimistic for even more reasons. I agree that these simplistic devices are going to give widely variable results and would point out that the legal departments of these companies are always going to err on having the device register a positive result (ie, go seek real medical help) as the downsides of that are you see a real medical provider and the company is at much less legal risk than the converse (you missed a diagnosis of sleep apnea, please give us a chunk of money for your sins and our loss of various important things).

There is a reason that becoming an FDA approved medical device is onerous and expensive. This stuff is hard.

Now, the end result might be fortuitously helpful. If it raises peoples suspicion of sleep apnea - a very common, very dangerous, easily treatable condition (if done professionally) then it is helping society at large.

I find the sleep info from my Jawbone UP3 useful. For one, being very competitive with even myself, I have an incentive to get the 8-hours of sleep I set as a goal. The UP app is very good, IMO. Shows me a shiny "100%" when I reach my goals and that's all the incentive I need. I'm easy.For two, having pets in the household, the UP3 helps me gauge how often they wake me up, if at all, and what quality sleep I'm getting when I fall asleep on the couch instead of in my bed. I'm not kidding. It happens so much that I wanted to know. The wake times are very accurate and I'm inclined to think so are the stated REM/light sleep/deep sleep periods, give or take 10%.The caveat, as someone else mentioned, is that I'm the poster child for placebos. Tell me something works and it'll probably work for me. Also, I got it for 30+ bucks on amazon and already got more than that back in healthcare incentives from my insurance, since it also counts steps and workout activity.

What I would like to see would be a comparison chart of independent sleep lab tests of actual sleep patterns/quality vs. what the various gadgets recorded.

I'm sorry, but sleep trackers (and to an extent, fitness trackers) fall into the "solution looking for a problem" category. They inundate consumers with a ton of pseudo-data with no clear way of utilizing or interpreting it. No one realized that sleep data was missing from their life until a company came along and told them, and not they've been convinced that it's integral to their wellbeing.

This.

How do you know you have a sleep problem? 'cause you're constantly tired despite spending 9+ hours in bed per night. There's no need for a sleep tracker for the general public.

While the same stands true for stuff like, GPS watches for runners, etc, at least there it holds a purpose to guide our intentional training. Tracking one's sleep... just seems futile unless there's something seriously out of step. ...and if there's a need to collect specific, individual data, there should likely be a medical professional involved.

The only real use I see for something like this is in sleep studies themselves. On the individual level, this just seems a futile thing beyond sating one's curiosity.

It can still be useful to rule some things out if you're trying to figure out hypersomnia or related symptoms of something. I had a couple doctors suggest I might have sleep apnea despite me being low-risk for it and now I can be pretty confident it's not the problem, letting me go down more productive diagnostic paths.

FWIW, I use Sleep As Android, which has a much richer feature set than everything I've compared it to so far, include support for pulse oximeters and chest straps as well as most open-standard wearables like Android Wear devices. Also recording any noises you make (snoring, gasps) and they have this weird ultrasonic sonar thing that works surprisingly well if your phone can do it.